This disclosure relates to a vaporized fuel processing apparatus including a canister equipped with an adsorbent adsorbing vaporized fuel generated in a fuel tank, a closing valve provided in a vapor path connecting the canister and the fuel tank to each other, and a purge path connecting the canister and the intake path of an engine to each other.
A pertinent conventional vaporized fuel processing apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2011-256778. The vaporized fuel processing apparatus according to Japanese Laid-Open Patent Publication No. 2011-256778 is equipped with a closing valve (control valve) provided in the vapor path connecting the canister and the fuel tank to each other. The closing valve is equipped with a dead zone region (valve-closing region) shutting off the vaporized fuel, and a conduction region (valve-opening region) allowing the vaporized fuel to pass; in the valve closing state, the fuel tank is maintained in a hermetic state; and, in the valve opening state, the vaporized fuel in the fuel tank is caused to escape to the canister side, making it possible to lower the inner pressure of the fuel tank. In the vaporized fuel processing apparatus according to Japanese Laid-Open Patent Publication No. 2011-256778, learning control is performed as follows. The degree of opening of the closing valve is changed in the opening direction at a predetermined speed from the valve-closing position; and when the inner pressure of the fuel tank begins to be reduced, the degree of opening of the closing valve is stored as the valve opening start position.
However, suppose, for example, the actual inner pressure of the fuel tank is in excess of the measurement range of the pressure sensor for detecting the inner pressure of the fuel tank. In this case, when the learning of the valve opening start position for the closing valve (control valve) is executed, it is impossible to correctly detect with the pressure sensor the timing with which the inner pressure of the fuel tank began to decrease. Thus, the valve opening start position for the closing valve (control valve) would be erroneously learned, resulting in a rather unstable control when performing the pressure control of the fuel tank by using the closing valve (control valve). Accordingly, there is a need for improved vaporized fuel processing apparatuses.